"These algae occur naturally and are risks to human health when their numbers are high.

"The toxins accumulate in the shellfish as they feed on the algae, temporarily making the shellfish dangerous to eat."

Eating shellfish with high levels of toxins may be fatal and children are more susceptible. Cooking does not destroy the toxins.

"The algal bloom is caused by two algal species: Gymnodinium catenatum, well known for affecting this region, but normally in autumn, and Alexandrium tamarense Group IV, which has not previously been detected in this area, but has affected the East Coast of Tasmania this summer."

Dr Veitch said people should not eat oysters, mussels, clams or pipis from the Huon Estuary, Port Cygnet or Port Esperance.

As a precaution, people should not eat scallops or the gut or organs of crab or rock lobster from this area.

"People should not eat the gut or organs of abalone from the Huon Estuary, including Port Cygnet."

PSP symptoms include tingling and pins and needles around the mouth and face, hands, arms and feet, unsteadiness and weakness, blurred vision and sometimes difficulty talking, swallowing or breathing.

"If you have these symptoms after eating wild seafood from, or near, the affected areas, get immediate medical attention."

"In instances such as this, when our routine tests alert us to a problem, commercial shellfish farms in affected area are closed until we're sure the shellfish have got rid of all toxins and are once again safe to eat.

"While these measures are vital to protect our health and safety, it is unfortunate this is affecting many of the same operators closed for the same reasons last year," Dr Veitch said.

Meanwhile, the East Coast of Tasmania is still affected by the toxic alga Alexandrium tamarense Group IV.

Dr Veitch said weekly monitoring had detected concerning levels of this algae in several areas recently.

"People should not eat wild-harvested oysters, mussels, clams or pipis, or scallop roe from the East Coast of Tasmania between Marion Bay and Waterhouse Island.

"Tests of rock lobster gut and organs (sometimes called tomaley) from this area have shown falling levels of algal toxins.

"While rock lobster gut and organs currently pose no risk to health, we recommend people do not eat these parts of rock lobster or crab from this or other areas; however, rock lobster flesh is safe to eat," Dr Veitch said.